Why Won't Simply Creating Lots of Marine Reserves Save Sea Life?

How is the world doing at conserving marine life? One common metric is the amount of ocean that governments have designated as protected areas. About 1.8% falls into that category, but fishing or other harvesting is banned in only 1%. Now, the most comprehensive and detailed analysis yet suggests that the marine conservation picture is even bleaker—and that a more accurate way of measuring progress is needed.

Graham Edgar of the University of Tasmania, Hobart, led a team that looked at 87 marine protected areas (MPAs) around the world. That’s a tiny fraction of the about 5100 MPAs on the books, but most lack enough data on sea life populations to be analyzed in detail. The researchers looked at the total estimated biomass of all fish within each of the selected MPAs, as well as the total weight of fish longer than 25 centimeters. (Larger fish tend to be targeted by fishing, as do valuable species such as sharks, groupers, and jacks.) They also tallied the total number of species of large fish and all fish in each MPA. Then, for comparison, they gathered data from 1022 sites where fishing is permitted around the world.

The analysis highlighted five features that appear essential for an MPA to score high on promoting fish biomass and diversity. The best performing reserves, as expected, have outlawed fishing and strictly enforced the ban. They are also relatively large and old, covering more than 100 square kilometers and established more than 10 years ago (giving the biota time to recover from any past fishing). In a statistical model, these four factors each contributed about the same amount to boosting the amount of fish. The fifth and most important predictor of success, however, was the MPA’s isolation from similar habitat, which makes them easier to police.

The comparison of MPAs to fished areas, however, produced a sobering result. About 60% of MPAs scored well on one or two of these key features, but appear to have fish populations that are no healthier than those found in fished areas. In contrast, MPAs that score well in three areas, including Coiba National Park in Panama, had on average 30% more fish and double the sharks of the fished areas.

Overall, the authors considered just nine of the MPAs (about 10%) to be effective, having four or more attributes of good governance and design. And the few reserves that got high marks in all five areas, such as the Kermadec Marine Reserve in New Zealand, had exponentially greater benefits, including nearly 2000% more sharks than in fished coastlines, they report in this week’s issue of Nature.

The takeaway message, the authors write, is that “global conservation targets based on area alone will not optimize protection of marine biodiversity. More emphasis is needed on better MPA design, durable management and compliance to ensure that MPAs achieve their desired conservation value.”

The study offers “a really good synthesis,” says fisheries biologist Trevor Branch of the University of Washington, Seattle. Previous studies, he notes, have looked at some of the five factors, but not in such a comprehensive way.

“What impresses me about the paper is that they have shown how key factors all need to be present [for reserves] to be effective,” says Elliott Norse, chief scientist of the Marine Conservation Institute in Seattle. Norse’s group is now developing criteria to recognize effective MPAs. Such efforts, he hopes, will become an incentive for countries to design effective MPAs and protect them, in part by conferring some prestige on the most successful efforts.

In a commentary in Nature, Benjamin Halpern of the University of California, Santa Barbara, calls the findings worrying, because “it is difficult for managers to achieve all five factors.” Most governments can’t create large or remote marine reserves, so they must focus on enforcement, which can be expensive. More research should be done on other possibilities, such as connecting MPAs into networks, Halpern wrote.